Electron-tube stabilized amplifying circuit



April 23, 1957 B. H. TONGUE ELECTRON-TUBE STABILIZED AMPLIFYING CIRCUITFiled June 7, 1955 OUTPUT INVENTORQ BEN mucus INPUT ATTORNEYS;

ant i'rnore particularly, re raaiqfre 'such techniques as'utilifziiigdegeneratioh f provide a new "and i prove meme -tribecathode, control gamma-scream H todes. In summary, this end is 9. Inc

United States Pa 1,756,031; ELECTRON TUBESTABILIZED AMPIJIFYING CIRCUITBenH. i*6n 1ie, vVestfiil, N. J. Application June 7, m ss-serial1%:512808 e'olaiin's. (01. 179471) "re electron-tube circuits r n w 'bodyin'gelectron tubes having at lea-st five electrodes, such as pentodes. n

u In many present-day electron- A or vacuum-tuberadiofrequencyiamplifier circuits, and p rt'eur' l p loying pento'des,deleterious: ef-t'unln'g and bandwidthif'aiiaition effects take "placeas "thega'in of the 'tube is varied. This ale-tuning eifect is caused byimproper neutralization of feedback between the outputandir'iputpirfeedback effects in pentodes and reso e in the screengrid-to-c'athode"circuit. V

An obiect of the present invention, accordingl'yfis'tb shallfn'ot beSubject to "either 255 the above' deleterious e'ifec'tso'fde-tiiningohbandiwidth When n.

A further object is to p rovide a newan p entode electron-tube circuit fth' at 's ir nulta'njeo 1 y pensates not only for"alhfeedbaclgeifectsiquency pentod'e anipl'ifieifs'but also foriie g'ativej sistance effectsresulting from the' triode' operation pen sesribe a circuit connectionfrom fthe 'f scr ground having negligible radio-fi e V by resonating outthe i' d tanc'eof'thefsc e input circuit through the anode-ito-s tradeand suppresscr-grid electrode-to-contiol-grid 615etrode capacitances,substantially sire undre d eighty degrass 'with respect to the phas e of theiradiofieguencyienergy fed from theoutput tothrbughthdaiicideto-cont rol-grid electrode capacitance.

, n q -k di iihtf.Nes s. wi llb j ir e f i iii iir anti will be moreparticularlypoiiited but in the appended claims The invention will nowbe describled in connection 'with the accompanying drawing the singlefigure' of v'vhich is aschematic circuit diagram illustrating theinvention in preferred fer-m. H

A conventional'pentode electron tube or vacuumtube, as of the beam type,is schematically shown at -1 provided with an electron-emitting cathodeelectrode 2, a controlgridelectrode 3, a screen-gridelectrode '4, asuppressor- 'grid ele'ctrod'e'S and a plate or 'anode'electrode 6. Asource of anode potential or voltage is applied between the anode sandthe cathode 2, the pos""' ve or B -lterininal of the voltage sourceheiiig'conn" ted, p 'fer'abl'y through a radio-fre'que'ncy choke, not shwn, ode 6, and the negative or B-tirriihzil Being co I throughcathode-load resistors 7 and '9 to'the cathode'Z. The B terminal may beconnected to ground, 'asis'hovv'n, if desired. The term groundfindeed,as utiliz'ed'in'tliis specification and in the claims, is'in'tendedtobonfiote 'iiot only actual earthin'g, but chassis or any otherreference potential. Inorder not to detract from ithe f'ature's ofnovelty, the well-known details'of'tlie voltage's'ourcesffor :the"electrodes and other circuit refinements'are not illustrated. i V vConnected between the anode 6 andlcathode Z is an outpufcircut Zm'puSimilarly, an input ircuit Z nes may be connected between the B'ftemiih'al a the centiol grid electrode 3 by 'conductojrsti andlfi,fespctively. The input and eut'pm circuitsai eshown in generalizedbl' shk-diagrmn form'sinee the presen invention ma be utilized with anydesired type of radio frequency circuits,

input and output circuits. "As "an 'il1tistration, 4 and output circuitsmay' comprise res ant a vvorks s'uch 'a'sQshurit or series-connected embinar ris ifi'du ctzlirice tiiidfc'apacitanee, "sir-awn. Tne',,,.mjb aj p'n'teue stage may be varied b'y varying the amount o'f 'hegative biasvol age applied 'rtoin a source of saga e potential -vie throughapotentiometer 11, and 'a 'd to th eantrergna electrode '3. 'I he r or12. 1s 'slrovvn aadhpied to ground by a lay-passe denser '13. The biasvoltage may, of' course, be co o'll'd autiimaticaily by fa'n automaticgain control circuit, as ell ever, fromthe plate or ano'de6 totli' Athrough the inherent anode toscFen-grid :electr'o'de "eapacitarice C 35and the'screen-grid"electfode to controlg rid electrode capacitance C'It'haslbefore scanneprised tomininiize the feedback aloii'gtli'e pathCnsQC-S'}; by jgrou n ding the screen-grid electrodef4. Miriiiniiiiig ofthe feedback effect alongthe'p'ath C 'lias'lpeen"attempted throughelaborate shielding 'h'etwen the grid anaem a connections. 7 v v-Untortur' ately, however, at the higherradio' freqiiencies above, say,tens of megacycles, the physi'c'al"s'tfictureiof the screen grid4 inconventional Pen'tods. and the I'lie and of the above desc'ribedconnection theref 'gr'cund, even iflrept veryshort, may present a subs't ntial inductive reactance Neutralization aloirglthepath Cps, Q e ythese P i r mas es i thuvs a bl t frequenciesin view of the factthat-this inductiye rea ssn P n i l. isi'lt isia tsfi s l vs hi d. e weep 1 2 M i? P??? thi awe :thP. f n si i Estate? Qpie sfisti.at.Pgi i e iqs qnqi s r -Phys 'ical structure of the screen grid 4 and the connectionthereof to ground produces the earlier-mentioned further circuit.

a negative input resistance of the tube, results in a change in theradio-frequency loading of the triode portion 2, 3, 4 of the pentode 1.This loading change will produce a corresponding change in the Q of theinput circuit Zinput and hence will result in an undesirable variationof the bandwidth of the input In accordance with the present invention,the matter of rendering the feed-back path cps, Csg ineffective and ofobviating the bandwidth-variation effect in the triode operation of theportion 2, 3, 4 of the pentode, is accomplished in the following way.Though it is not possible to ground the physical center of the screengrid 4 directly,

since the grid is within the envelope 1, this result is effectivelyachieved electrically by resonating the inherent inductance L of thestructure of the screen grid 4 and the inductance of the physicalconnection to ground from the terminal of the tube socket, not shown, inwhich the tube 1 is mounted, with appropriate series-connectedcapacitance C. This resonance at the desired radio frequency places thescreen grid 4 at radio-frequency ground and effectively shields thecapacitance cps from the capacitance Csg, thereby preventing feedbackenergy from passing therebetween. In addition, however, this resonancehas caused the impedance between the screen grid 4 and ground to changefrom a reactance, the effect of which caused a negative inputresistance, into substantially a low resistance with negligiblereactance. now negligible impedance between the screen grid 4 andground, the radio-frequency loading of the triode portion 2, 3, 4 of thepentode 1 will not change with change in gain of the pentode and theundesirable bandwidth-variation effect is simultaneously substantiallyeliminated, also.

It now remains to vitiate the effects of the feedback path including thecapacitance Cpg, which may have a very small capacitance value of, forexample, 0.02 micro- Since there is microfarad. This could theoreticallybe done by utilizving a large parallel-connected inductor; but, inactual practice, particularly at high frequencies, it is not feasible toconstruct such a large inductor that willnot inherentlyhave'dis'tributed capacitance which is even greater than thesmall-valued capacitance cpg. In ac- 'cordance with the presentinvention, therefore, an entirely different technique is employed. Acircuit connection 16 is made from the suppressor-grid electrode 5 toground through an inductance Ll of sutficient value to produce apredetermined shift in the phase of the radiofrequency energy of thedesired frequency fed from the anode 6 through theanode-to-suppressor-grid electrode 1 capacitance C; to the suppressorgrid 5. The amount of phase shift required is that which will bring theenergy fed from the suppressor grid 5 to the control grid 3 through thesuppressor-grid electrode-to-controlgrid electrode capacitance C2 insubstantially phase opposition to (i. e. substantially one-hundredeighty degrees out of phase with) the energy coupled back from theoutput to the input through the interelectrocle capacitance Cpg- Theone-hundred eighty degree out-ofphase voltage at the suppressor grid 5will cause a current to flow through the suppressor grid-to-control gridcapacitance C: to the control grid 3 which is substantially equal andopposite to the current flowing from the anode 6 to the control grid 3through capacitance Cpgflows from the output to the input circuit. Toachieve such a phase shift, the reactance of the inductance Li at thedesired high frequency will be made smaller than the reactance of eitherof the interelectrocle capacitances Ci or C2.

The result is that substantially zero net feedback current As anillustration, the above results can be achieved with a 6CB6-type pentodeoperating with input and output circuits tuned in the neighborhood ofabout 200 megacycles with an inductance L1 formed of about a one-inchloop of number twenty-four wire. The screengrid resonating capacitance Cmay have a value of about 39 micromicrofarads and the length of theconductorlead 15 may be about one-eighth of an inch.

At much lower frequencies, the reactance of the screen grid 4 and itsconnection 15 to ground may be sufficiently negligible that a directshort connection 15 may suffice without the necessity for the resonatingcapacity C. While the plate-to-control grid feedback will then not bereduced to so low a value as can be attained with the resonatingcapacity C, the results may, in some instances, be adequate. It is alsoto be understood that external neutralizing elements could be employedto replace the interelectrode capacitances and the suppressorto-groundinductance, but since such external elements would increase the tubeinput and output capacitance and thus reduce the gain, this is not apreferred construction.

Further modifications will occur to those skilled in the art and allsuch are considered to fall within the spirit and scope of the inventionas defined in the appended claims.

What is claimed is:

1. In an electron-tube circuit for operation at a predetermined radiofrequency having at least five electrodes, namely, an anode, a groundedcathode, a control-grid electrode, a screen-grid electrode and asuppressor-grid electrode, and radio-frequency input and output circuitsconnected from the cathode to the control-grid electrode and to theanode, respectively; the combination of a circuit connection from thescreen-grid electrode to ground having negligible impedance at the saidpredetermined radio frequency, and a circuit connection from thesuppressor-grid electrode to ground having an impedance of 'suflicientreactance at the said predetermined radio frequency to shift the phaseof the radio-frequency energy fed from the said output circuit to thesaid input circuit through the anode-to-suppressor-grid electrodecapacitance and the suppressor-grid electrode-to-control-grid electrodecapacitance substantially one hundred eighty degrees with respect to thephase of the radio-frequency energy fed from the said output circuit tothe said input circuit through the anode-to-control-gr id electrodecapachance.

tance from the screen-grid electrode-to-control-grid electrodecapacitance, means for presenting a negligible impedance at the saidpredetermined radio frequency between the screen-grid electrode andground, and a circuit connection from the suppressor-grid electrode toground having an impedance of sufficient reactance at the saidpredetermined radio frequency to shift the phase of the radio-frequencyenergy fed from the said output circuit to the said input circuitthrough the anode-to-suppressor- 3. In an electron-tube circuit'for'operation at a predetermined radio frequency having at least fiveelectrodes,

namely, an anode, a grounded cathode, a control-grid electrode, ascreen-grid electrode and a suppressor-grid electrode, andradio-frequency input and output circuits connected from the cathode tothe control-grid electrode and to the anode, resspectively; thecombination of a circuit connection from the screen-grid electrode toground provided with capacitance of suificient value to resonate at thesaid predetermined radio frequency with the inductance in the saidcircuit connection, including the inductance of the screen-gridelectrode itself, in order not only to ground the screen-grid electrodebut to do so through a circuit of negligible impedance at the saidpredetermined radio frequency, and a circuit connection from thesuppressor-grid electrode to ground provided with inductance ofsufficient value to shift the phase of the radio-frequency energy fedfrom the said output circuit to the said input circuit through theanode-to-suppressor-grid electrode capacitance and the suppressorgridelcctrode-to-control-grid electrode capacitance substantially onehundred eighty degrees with respect to the phase of the radio-frequencyenergy fed from the said output circuit to the said input circuitthrough the anode-to-control-grid electrode capacitance.

4. In an electron-tube circuit for operation at a predetermined radiofrequency having at least five electrodes, namely, an anode, a groundedcathode, a control-grid electrode, a screen-grid electrode and asuppressor-grid electrode, and radio-frequency input and output circuitsconnected from the cathode to the control-grid electrode and to theanode, respectively; the combination of a circuit connection from thescreen-grid electrode to ground having negligible impedance at the saidpredetermined radio frequency, and a circuit connection from thesuppressor-gridelectrode to ground provided With inductance of reactanceat the said predetermined radio frequency less than the reactance of theanode-to-suppressorgrid electrode capacitance and of the suppressor-gridelectrode-to-control-grid electrode capacitance but sufficient to shiftthe phase of the radio-frequency energy fed from the said output circuitto the said input circuit through the anode-to-suppressor-grid electrodecapacitance and the suppressor-grid electrode-to-control-grid electrodecapacitance substantially one hundred eighty degrees with respect to thephase of the radio-frequency energy fed from the said output circuit tothe said input circuit through the anode-to-control-gn'd electrodecapacitance.

5. In an electron-tube circuit for operation at a predetermined radiofrequency having at least five electrodes, namely, an anode, a cathode,a control-grid electrode, a screen-grid electrode and a suppressor-gridelectrode, and radio-frequency input and output circuits connected fromthe cathode to the control-grid electrode and to the anode,respectively; the combination of a circuit connection from thescreen-grid electrode to ground having negligible impedance at the saidpredetermined radio frequency, a circuit connection from thesuppressor-grid electrode to ground having an impedance of sufiicientreactance at the said predetermined radio frequency to shift the phaseof the radio-frequency energy fed from the said output circuit to thesaid input circuit through the anode-to-suppressor-grid electrodecapacitance and the suppressor-grid electrode-to-control-grid electrodecapacitance substantially one hundred eighty degrees With respect to thephase of the radio-frequency energy fed from the said output circuit tothe said input circuit through the anode-to-control-grid electrodecapacitance, and a cathode load connected between the cathode and groundand part only of which is by-passed to ground.

6. In an electron-tube circuit for operation at a predetermined radiofrequency having at least five-electrodes, namely, an anode, a cathode,a control grid electrode, a screen-grid electrode and a suppressor-gridelectrode, and radio-frequency input and output circuits connected fromthe cathode to the control-grid electrode and to the anode,respectively; the combination of a circuit connection from thescreen-grid electrode to ground having negligible impedance at the saidpredetermined radio frequency, a circuit connection from thesuppressor-grid electrode to ground provided with inductance ofreactance at the said predetermined radio frequency less than thereactance of the anode-to-suppressor-grid electrode capacitance and ofthe suppressor-grid electrode-to-control-grid electrode capacitance butsuflicient to shift the phase of the radio frequency energy fed from thesaid output circuit to the said input circuit through theanode-to-suppressor-grid electrode capacitance and the suppressor-gridelectrode-to-control-grid electrode capacitance substantially onehundred eighty degrees with respect to the phase of the radio-frequencyenergy fed from the said output circuit to the said input circuitthrough the anode-to-control-grid electrode capacitance, and a cathodeload connected between the cathode and ground and part only of which isbypassed to ground.

References Cited in the file of this patent UNITED STATES PATENTS2,093,094 Peterson Sept. 14, 1937 2,200,055 Bornett May 7, 19402,533,020 Knol Dec. 5, 1950

